As Mexico’s military staged its annual Independence Day parade in September, spectators filled the main square of Mexico City to cheer on the armed forces. Nearly 2,000 miles away in Washington, U.S. officials were also paying attention.

But it was not the helicopters hovering overhead or the anti-aircraft weapons or the soldiers in camouflage that caught their attention. It was the man chosen to march at the head of the parade, Gen. Moises Garcia Ochoa, who by tradition typically becomes the country’s next minister of defense.

The Obama administration had many concerns about the general, from the Drug Enforcement Administration’s suspicion that he had links to drug traffickers to the Pentagon’s anxiety that he had misused military supplies and skimmed money from multimillion-dollar defense contracts.

In the days leading up to Mexico’s presidential inauguration on Dec. 1, the United States ambassador to Mexico, Anthony Wayne, met with senior aides to President Enrique Pena Nieto to express alarm at the general’s possible promotion. That back-channel communication provides a rare glimpse into the U.S. government’s deep involvement in Mexican security affairs — especially as Washington sizes up Pena Nieto, who is just two months into a six-year term. The U.S. role in a Mexican Cabinet pick also highlights the tensions and mistrust between the governments despite public proclamations of cooperation and friendship.

“When it comes to Mexico, you have to accept that you’re going to dance with the devil,” said a former senior DEA official, who requested anonymity because he works in the private sector in Mexico. “You can’t just fold your cards and go home because you can’t find people you completely trust. You play with the cards you’re dealt.”

A former senior Mexican intelligence official expressed similar misgivings about U.S. officials.

“The running complaint on the Mexican side is that the relationship with the United States is unequal and unbalanced,” said the former official who, like others interviewed for this article, spoke anonymously to discuss diplomatic and security exchanges. “Mexico is open with its secrets. The United States is not. So there’s a lot of resentment. And there’s always an incentive to try to stick it to the Americans.”

Washington’s concerns about Garcia Ochoa — which several officials cautioned were not confirmed — come as both governments grasp for new ways to stem the illegal flows of drugs, guns and money across their borders.